Wave generation and modulation



March 28, 1939. K. FRITZ ET AL WAVE GENERATION AND MODULATION Filed June 4 1956 2 Sheets-Sheet l #K, T 40 H I 6 K pw fqg ll 41 fimwww A? n 07. 00 "MW Mp BC mm E n M G a mm a A N m C a I .HD U mm HM m l m an H mm M INVENTOR KARL FRITZ AND WILHFLM RUNGE BY Q -LQHJ CM FREQUENCY ATTORNEY INPUT March 28, 1939. K. FRITZ ET AL WAVE GENERATION AND MODULATION Filed June 4-, 1936 2 Sheets-Sheet 2 INVENTOR KARL FRITZ AND WILHELM RUNGE BY Z )1 ml/x/ ATTORNEY Patented Mar. 28, 1939 NITE s'l if i E assigncrs to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application June 4, 1936, Serial No. 83,496 In Germany May 18, 1935 13 Claims. (Cl. 179-471) The present invention is concerned particularly with circuit organizations adapted to modulate magnetrons (Habann tubes).

Modulation circuit arrangements adapted to use with magnetrons are known in the prior art in which the modulation waves are superposed either upon the magnetron anode potential or upon the exciting current of the main magnet field. These circuit schemes involve a number of shortcomings. In case of variation of anode potential in consonance with the modulation waves, frequency variations inside a wide range are unavoidable. In case of variation of the main magnetic field, frequency variations con- 16 jointly with hysteretic losses and other actions associated with'distortions and energy losses are produced.

The particular form of the paths of the electrons in the magnetron precludes, as a general 20 rule, the mounting of auxiliary electrodes for control purposes between the cathode and the anode of the magnetron. For this reason, separate control or modulation schemes have been disclosed in the prior art (United States application 11,096 filed September 18, 1935) in which a magnetron containing four anodes or anode groups is employed in such a manner that two opposite segment groups are impressed with the control alternating voltages, while the other two groups deliver the amplified useful alternating potentials. These circuit organizations have proved successful. However, the anode circumference is covered up unnecessarily, with relatively large control electrodes to the detriment of the energy-absorbing useful anodes, and as a result the cooling conditions become unfavorable.

Modulation circuit schemes have also been disclosed in the earlier art which comprise tubes furnished with specially formed auxiliary electrodes posteriorly of or adjacent to the cathode, in other words, not between anode and cathode. (See United States application #50,128 filed November 16, 1935.) While it is true that modulation circuit organizations of this kind have proved quite satisfactory, it is nevertheless a fact that when ultra-short waves are concerned it becomes extremely difficult to accommodate the said auxiliary electrodes adjacent to or posteriorly of the cathode.

Hence, in order to carry into practice the idea underlying this invention, recourse is had to magnetron tubes in which the auxiliary electrodes are mounted either in a plane laid through the split between the anodes, more particularly at the same distance from the cathode as the anode,

or else in the rear of the anode, the latter bein in such a case, of course, grid or wire-shaped. Tubes. of this construction offer no constructional difiiculties even where extremely short waves are dealt with, and they are capable of great loads. 5

To be sure, the disposition of auxiliary electrodes between, or posteriorly of, the anodes in magnetrons has been disclosed in German Patent #428,547. The purpose of these auxiliary electrodes in this patent being to shut the anode 10 body so as to prevent electrons from fiying across the anode splits, and bombarding the wall of the vessel.

The exciting and modulation circuit organization of the presentinvention has the character- 15 istic feature that magnetron tubes are used in which auxiliary electrodes are mounted between or posteriorly or between and posteriorly of the optionally apertured anodes, and that the control or modulation oscillations are fed to the said 20 auxiliary electrodes.

Now, the said auxiliary electrodes may be made to act either by virtue of magnetic or electric action. If the auxiliary electrodes are arranged to insure electrical control of the discharge action 25 or process, they will preferably have to be impressed with a constant negative biasing potential in order that the source of modulation or control potential may not be loaded because of the finite resistance of the discharge path between the 30 auxiliary electrode and the cathode.

If it is intended to use magnetic control action to be brought upon the discharge process, then the auxiliary electrodes will have to be designed linear or more particularly filamentary, and to 35 be provided with bilateral connections in order that the modulation currents may be conducted through the auxiliary electrodes.

The use of the basic idea of this invention is by no means confined to the modulation of high 40 frequency oscillations with, say, audio frequency voice oscillations. In fact, the circuit organization here disclosed may to the same advantage, be used for the purpose of modulating and controlling the radio frequency production in a mag- 45 netron tube itself, and this by the aid .of a frequency which is equal to the natural period of the associated oscillatory circuit, or at least bears an integral relation thereto. In the last named instance, most suitably an even number of aux- 5 iliary electrodes will be provided, the latter being combined in pairs or groups in such a way that these groups at all times present to one another voltages that are different as to'phase and amplie as In Figures 1a, 2a, and 3a.- are shown by way of example three novel modulation circuit organizations. Figures 1, 2, and 3 are perspective views of electrode assemblies for the tubes comprised in the said modulation circuit organizations; while Figures 4, 5, and 6 are curves showing graphically the operation characteristics of the tubes used in the circuit organizations.

Figures 1 and 1a show a magnetron Ill provided with a split anode A1 and A2. In the slits or splits are filamentary auxiliary electrodes H1 and H2 which are conductively interconnected at one end by way of a conductor B and at the other end by way of the secondary winding of a modulation transformer M. In the center of the concentric disposition is the cathode K energized by any source UK. The electrons issuing from the cathode K and accelerated by the anode potential U. are caused to bend subject to the influence of a magnetic field produced by the winding H. The distribution of the electron emission current at radio frequency rhythm is accomplished by the radio frequency alternating voltages which are active primarily in the direct neighborhood of the slit and which have a governing influence upon the trajectory or path of the electrons.

In addition to such radio frequency distribution control action, the value or amplitude of the oscillatory current in the output circuit N is also subjected to a steady variation by the novel means of this invention. To accomplish this control or modulation a modulation current supplied by transformer M is passed through the series connected auxiliary electrodes I-I1 and H2 which produces a magnetic field which influences the high frequency oscillatory process and the intensity of the oscillatory current in accordance with the frequency and the amplitude of the modulation oscillations. For reasons which appear more in detail hereinafter the auxiliary electrodes H1 and H2 are biased relative to the cathode K by a source UH (Figure 1a) connecting a point on the secondary of M to the oathode K.

In Figures 2 and 2a we have illustrated another modulation scheme comprising the use of an electrically controlled tube. The two anode segments A1 and A2 of this tube II] are apertured. In other words, they either have the nature or form of grids or of wire nettings. Posteriorly of the anodes are two auxiliary electrodes H1 and H2. The apertured anodes are connected by way of an oscillation circuit N which, in turn, is united with the positive pole of an anode potential source UA. The auxiliary electrodes H1 and H2 are directly connected with each other either inside or outside the tube. Both auxiliary electrodes are impressed with the same, normally negative, biasing potential from a source UH. The modulation or control waves are superposed upon this biasing voltage by means of the modulation transformer M from any source.

Figures 3 and 3a show a pilot exciter organization. This circuit scheme may either be operated in such a way that it acts like a completely master controlled amplifier for radio frequency or that it is made to operate inside the range of forced oscillations (entrainment range) by choosing the working conditions of the tube arrangements so that they will be just about at the point of incipient oscillations. By separate control voltages, preferably of the same frequency, conditions may then be made so that, for the correct phase of the control oscillations relative to optionally self-excited oscillations, the oscillatory current will be started with surficient power.

In order to carry into practice these or similar circuit organizations, recourse may be had to a four-split magnetron as shown in Figures 3 and 3a. Pairs of opposite anodes A1 to A4 inclusive are combined or connected to form two groups of electrodes symmetrically arranged about the cathode K. The two groups are united or connected as shown with an output circuit N which will deliver the ensuing produced or amplified oscillations. To control the discharge process at radio frequency rhythm, four auxiliary electrodes H1 to H4 inclusive are provided and are likewise combined into two groups symmetrically arranged relative to K and are fed in phase opposition from a radio frequency source of control potential St. The wave energy impressed on St may be of the same frequency or else of a frequency which roughly bears an integral relationship to the natural frequency to which the output circuit N united with the generator is tuned. The working voltages, that is, UH, UA, and UK, should be chosen in a similar manner as in the circuit organization shown in Figure 2.

In Figure 4 we have shown the modulation characteristic that a magnetron tube with four anode segments in which only two electrically acting linear electrodes, such as H1 and H2 of Figure 1, in two opposite splits or apertures are mounted. The purpose of this curve is to show that for carrying into practice the basic idea of this invention, all slits between anodes must be supplied with auxiliary electrodes.

If the operating conditions are properly chosen (anode potential and magnetic field), conditions can be made so that the radio frequency cLurent J will undergo practically no alterations in the presence of variations of the modulating voltage UH of the auxiliary electrodes H1 and H2 in the range of values of the anode and the cathode potentials. It is only when the auxiliary electrode potential becomes lower than the cathode potential that the oscillation current J will be caused to decrease to around zero value in a steady or linear manner. The modulation characteristic as shown by the curves for negative values of UH is free from points of unsteadiness and unevenness. The constant negative biasing potential of the auxiliary electrodes is chosen preferably and advantageously equal to the absolute value of one-half the anode potential. The modulation voltages whose crest is also chosen equal to one-half the effective anode voltage is superimposed upon the auxiliary electrode biasing voltage. Hence, it is thus feasible to master the diflicult problem of thoroughly modulating a magnetron under satisfactory conditions, in the absence of dissipation, between zero and maximum of the oscillation current, in a way practically free from distortions. The values here indicated have proved particularly appropriate by practical experiments. However, the ways and means of carrying the basic idea of this invention into practice is by no means dependent upon certain voltage values or certain voltage relations of the electrodes to one another.

No appreciable drop in efficiency happens if the width of the slit, etc., are altered. By the symmetric position of the auxiliary electrodes to the live main anode, neutralization is insured from the very outset.

In Figure 5 is shown the shape of the partial anode currents Jal and Ja2 of a magnetron tube operating as a master excited amplifier. What was used was a tube similar to Figure 3 connected as illustrated in Figure 3a.

In order to be able to operate at maximum emciency, the Working point upon the overall anode current plotted against magnetic field characteristic is so chosen that, in uncontrolled condition, in other words, when the auxiliary electrodes are at cathode potential (UH=) only a minimum anode current will arise as indicated at point I. If the auxiliary electrodes which are also connected in two groups are impressed. with phase opposed (push-pull) alternating control potentials idUH, then, according to the phase and the size of the auxiliary electrode potential, the radio frequency current of one anode group will rise and that of the other group will decline, and vice versa. In this way, an extremely low total anode feed (quiescent) current is caused to flow, and yet very high transient current impulses are provided, in the presence of greater positive or negative control alternating potentials. The efiiciency is quite satisfactory if the operating point is chosen at point I.

If the operating point is shifted to the middle, point II, of the anode radio frequency, (Ja) against field strength (F) characteristic, there is obtained alternately linear rise of current and decline of current in the two anode segment groups A1, A2, and A3, A4 as indicated by the broken lines Ja.

Working point III which involves an always relatively high anode feed current is poorly suited for the generation of oscillations inasmuch as in choosing this Working point the tube would be permanently loaded by a comparatively high anode direct current with the result that the alternating current yield of the tube would stay low in View of the limited thermal load carrying capacity of the anode and the cathode. The anode current Ja when the tube operates on point III, has been indicated bythe dotted curve We claim:

1. In a signalling system in combination, a magnetron tube having a field producing means, a cathode and a pair of like anodes connected by a source of direct current potential to said cathode and connected together by an alternating current circuit in which oscillations are produced, a pair of similar control electrodes located back of said like anodes, means for applying a negative potential tosaid control electrodes relative to said cathode and means for superposing modulating potentials on said negative potential.

2. A signalling system as recited in claim 1 wherein said pair of like anodes connected together by an alternating current circuit are connected in push-pull relation by said alternating current circuit.

3. A system as recited in claim 1 wherein said first named means comprises a direct connection between said control electrodes, and, a source of direct current and a modulation reactance connecting said control electrodes to said cathode.

4. A system as recited in claim 1 wherein said pair of like anodes connected together by an alternating current circuit are connected in pushpull relation and wherein said first named means comprises a direct connection between said control electrodes, and, a source of direct current and a modulation reactance connecting said control electrodes to said cathode.

5. In a signalling system the combination of Wave energy producing means comprising an electron discharge tube including an electron system located in a magnetic field of substantially fixed strength said electron system including a filamentary cathode, a pair of control electrodes and a pair of anodes all disposed about said cathode as an axis, said control electrodes being spaced from said cathode at least a distance substantially of the order of the distance of said anodes from said cathode, an alternating current circuit tuned to the frequency at which it is desired to produce wave energy connecting said anodes together, a source of direct current potential connecting a point on said alternating current circuit to said cathode, a second alternating current circuit connecting said control electrodes together, and means for impressing wave energy on said second alternating current circuit for controlling the character of the Wave energy produced.

6. In a signalling system the combination of Wave energy producing means comprising an electron discharge tube including an enclosure member located in a magnetic field of substantially fixed strength and enclosing a filamentary cathode, a pair of control electrodes and a pair of anodes disposed about said cathode as an axis, said control electrodes being spaced from said cathode a distance at least equal to the distance of said anodes from said cathode, an alternating current circuit tuned to the frequency of the wave energy to be produced connecting said anodes together, a source of direct current potential connecting a point on said alternating current circuit to said cathode, a second alternating current circuit connecting said control electrodes together, a source of direct current potential connecting a point on said last named alternating current circuit to said cathode, and means for impressing wave energy on said second alternating current circuit to control the character of the wave energy produced.

'7. A signalling system as recited in claim 6 wherein the absolute value of said last named direct current potential is substantially equal to one-half of said first named direct current potential.

8. A system as recited in claim 5 wherein said anodes are connected in push-pull by said first named alternating current circuit.

9. A system as recited in claim 6 wherein said control grids are tied together.

10. A system as recited in claim 6 wherein said anodes are connected in push-pull relation by said first named alternating current circuit and wherein said control grids are tied directly together.

11. A modulation system comprising in combination, wave energy producing means comprising an electron discharge tube including a filamentary cathode, a split anode electrode system comprising circular plate elements disposed about said cathode as an axis, a pair of control electrodes located in the openings between said anode electrodes, means for producing a magnetic field of substantially constant strength in which said electrode system is located, an alter- .nating current circuit tuned to the frequency of the wave energy it is desired to produce connecting said anodes in push-pull relation, a source of direct current potential connecting a point on said alternating current circuit to said cathode, and means for modulating the wave energy produced comprising a modulation frequency reactor connecting said control electrodes in series, and means for impressing modulating potentials on said modulation frequency reactor.

12. In a modulation system an electron system comprising a filamentary cathode, a pair of gridlike anode electrodes symmetrically located about the axis of said cathode, a pair of platelilse control electrodes symmetrically located about said cathode as an axis, said. control electrodes being spaced from said cathode a distance greater than the spacing of said anodes from said cathode, means for producing in. the space surrounding said electron system a magnetic field of substantially constant value, an alternating current circuit tuned to a relatively high frequency connecting said anode electrodes in pushpull relation, a source of direct current potential connected between a point on said alternating current circuit and the cathode of said tube, means tying said control electrodes together, a modulation frequency reactor and a source of direct current potential connecting said control electrodes to said cathode, and means for impressing modulating potentials on said modulation frequency reactor.

13. A system as recited in claim 1 wherein the absolute value of said last named potential is substantially equal to one-half of said first named potential.

KARL FRITZ. WILI-IELM RUNGE. 

